This scary looking beastie is the European Green Crab. It's not native to Maine, but they started coming over attached to the hulls of wooden trading ships a hundred years ago. But it's only just in the last two years that there's been a massive spike in the crabs' population, devastating the local clam-fishers.

According to Foster's Daily Democrat:

Fishermen and scientists in the state of Maine have noted a marked
increase in the numbers of green crabs over the last two years, which
are taking a dramatic toll on the ecosystem, notably the clam and
soft-shell crab population.

This translates into an economic
problem as well. In 2012, the Bangor Daily News reported that shell clam
diggers brought in over $15.5 million in revenue. An explosion in the
green crab population is not a good thing for their business.

Why is the problem getting worse in Maine?

One factor is that
the crab has no natural predators. However, this is not new. The other
more interesting theory is that a warming of the ocean temperature may
be a factor. Experts from the Maine Department of Marine Resources
report the Gulf of Maine saw warmer temperatures during 2012.

The Green Crabs have almost no natural enemies, apart from sea bass, and Maine locals aren't interested in eating them, because they're too small.